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Risk Management Activities - Impacts of currency rate risk (Details) - Currency risk - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of credit risk exposure [line items] |  |  |
Sensitivity analysis, Net earnings increase (decrease) | $ (12) | $ (24) | $ (20)
Sensitivity analysis, OCI gain | 1 | 2 | 0
U.S. Dollars |  |  |
Disclosure of credit risk exposure [line items] |  |  |
Sensitivity analysis, Net earnings increase (decrease) | (8) | (18) | (13)
Sensitivity analysis, OCI gain | 1 | 2 | 0
Australia, Dollars |  |  |
Disclosure of credit risk exposure [line items] |  |  |
Sensitivity analysis, Net earnings increase (decrease) | (4) | (6) | (7)
Sensitivity analysis, OCI gain | $ 0 | $ 0 | $ 0

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